The general construction of commercially successful roller rotary reamers are shown in the applicant's Australian patents 594885 and 675186.
Australian patent 675186 describes a rotary roller reamer in which the pressure of the environment surrounding the reamer is applied to the lubricant supplied to the roller bearing surface by means of a freely floating piston contained in a cylindrical passage. This results in significantly improved lubrication and reduction of the ingress of contaminant material to the bearing surface. Whilst the rotary roller reamer described in Australian patent 675186 has a significantly extended life for the wear components the present invention seeks to provide further improved rotary roller reamer.
The objective of the pressure equalization system described in Australian patent 675186 is to reduce or eliminate the differential pressure across the sealing device provided between the roller and spindle on which it is mounted to prevent ingress of contaminant to the bearing region. The sealing device is often an O-ring or a more complex seal. In the case of O-rings and most other types of seal, a reduction of the differential pressure will reduce the contact pressure between the seal and the sealing surface. This in turn will assist in reducing wear and subsequent seal failure.
In the rotary roller reamer described in Australian patent 675186 the lubricant is supplied to the bearing surface through apertures from a central passage which supply the lubricant to a flat formed on the spindle that effectively provides a passageway extending along the bearing. Thus, the lubricant reaches the seals largely by being transmitted along the bearing surface. It has been recognized in this configuration the bearing itself acts as a pressure barrier partly because of the rotation of the roller at around three times the speed of the drill string. Additionally in the arrangement described in Australian patent 675186 the thrust bearing ball race is also interposed between the supply of lubricant and the seal at one end of the roller. This also acts as a pressure barrier.